Technical Field
The present invention relates to methods for modulating color temperatures, and more particularly to a method that uses blackbody radiations as benchmarks to modulate LEDs to simulate specific color temperatures in the visible band, thereby producing light that has good color rendering property.
Description of Related Art
Traditionally, in an adjustable light-emitting device that modulates color temperatures using plural red, green and blue LEDs, adjustment of color temperature is usually achieved according to chromaticity coordinates or CRI (Color Rendering Index). However, the traditional red, green and blue LEDs usually have narrow spectral bandwidths, and there are only a few kinds of high-efficiency phosphor can work with them. Under the circumstances that only using three to five different wavelengths to modulate different color temperatures, it is difficult to achieve good color rendering property in different color temperatures.
The traditional method to compute CRI is that comparing with the reference to colors of reflected light of 14 different reference material under illumination from a subject light source. Although the application of CRI is getting more and more extensive, the conformity of the reference material has increasingly incurred doubts from experts in various fields. The key issue lies on metamerism that prevents the reference values of the all 14 different colors for CRI from meeting the requirements for good color rendering property at the same time. This may hinder CRI from accurately expressing the color rendering property of the object light source. Hence, there is a need for a method for modulating color temperatures that is accurate and independent of the reference or standard for CRI.